UC Berkeley

This work addresses two major unsolved questions in the field of C. elegans neuroscience and stress biology. First, are glia of the worm able to regulate the heat shock response (HSR) in a non-cell autonomous manner. Second, are these glia also required for regulation of such a response.

In the first chapter, I introduce concepts relevant to the works herein presented. Aging induces cellular dysfunction partially by the decline of protein homeostasis stress responses. When this function is restored, animals live longer and healthier. Although stress responses are specialized to the functions of individual organelles, signaling can be transmitted from neural cells to peripheral tissues in a protective manner. The role for glia, the non-neuronal cells of the brain, in this process is not well described. Glia, including astrocytes, closely regulate homeostasis of brain tissues, including by immune and stress responses. As this homeostasis deteriorates with age, risk of neurodegenerative disease increases. Most neurodegenerative diseases are characterized by the accumulation of protein misfolding, including Alzheimer’s Disease (AD). AD patients, among those with other so-called “tauopathies,” exhibit misfolding of the microtubule-associated protein tau. Tau abnormalities are associated with neuronal dysfunction, but their role in organellar stress response induction has not been well characterized.

In the second chapter, I examine the mechanism by which the cephalic sheath (CEPsh) glia of the nematode C. elegans coordinate the HSR across tissues to increase stress resistance, lifespan, and immune tolerance. When the main regulator of the heat shock response, heat shock factor 1 (hsf-1), is over-expressed in the four CEPsh cells, I identify an increase in lifespan alongside peripheral induction of heat shock chaperones and an increase in heat stress tolerance. The mechanism by which this non-cell autonomous communication occurs is independent of the neuronally-coordinated HSR system, operating without requirement for the AIY interneuron or serotonin synthesis. The response is also transmitted independent of previous glial-derived signals, which had originated from UNC-31-mediated dense core vesicles, and instead relies on transmission by UNC-13-mediated small clear vesicles. However, there is no clear requirement for a singular neurotransmitter that might be contained in such vesicles. In the periphery, hsf-1 itself is required, as the insulin signaling factor daf-16 in a partial manner. In addition, immune factors are highly upregulated in CEPsh glial hsf-1 animals, which are resistant to pathogenic bacteria. Taken together, I here identify a unique signaling mechanism by which CEPsh glia specifically modulate heat stress signaling.

In the third chapter, I investigate the endogenous role for CEPsh glia in regulation of the HSR. I first characterized by imaging several types of developmental mutants causing CEPsh glial ablation. I next tested these strains for heat stress tolerance and found that mutants for the development of all four CEPsh cells, but not ventral CEPsh glia alone, displayed increased thermotolerance relative to wild type animals. This did not occur concomitant with increased chaperone induction. Further, I identified a requirement for CEPsh glia in neuronal HSR signaling, for both lifespan extension and for thermotolerance induction. These data suggest that CEPsh glia are naturally strong regulators of the heat shock response, and that such regulation may occur in a positive and negative fashion, in close interaction with neurons. More work is necessary to understand the dynamic nature of this regulation, and through what mechanism it occurs in the glial and neuronal systems.

In sum, I here describe several unique roles and signaling mechanisms concerning the heat shock response for the CEPsh glia of C. elegans. These data, in combination with prior works, demonstrate that CEPsh glia flexibly and specifically respond to organelle-targeted stressors, coordinating an organismal response to that unique cue. In the case of heat stress, such cues may include heat or other protein misfolding insults, as previously shown, but also pathogen stress. Further, CEPsh cells serve a larger role supporting neuronal HSR signaling, which remains unprobed. Taken together, I show that CEPsh glia are both sufficient to regulate organismal heat stress and necessary to ensure endogenous HSR function range. These works will shed light on how neuronal and glial aging impact organismal health and longevity, particularly in the case of neurodegenerative diseases.